In article Vwjse.6938$El.2117@pd7tw1no, Ken Weitzel wrote:

Rick wrote:

snip

Wondering if your building might possibly be on one of those
flat rate electric water heating plans? Where the hydro
utility puts a signal on the line to turn off the heaters
during peak demand periods?

If so, then that plus a perhaps marginal electrolytics in
the radio might be an explanation.

Ken & Rick-

Of course it would help if you had laboratory equipment to analyze the
spectrum of the power line signal, as well as to determine how the noise
was getting into the radio.

Something is generating a signal that is somehow coupling into the radio
and coming out the speaker. Ken's idea suggests that it might be getting
into the radio through the power line, but either at the intermediate
frequency of the radio or through the audio section, either directly or
by rectification.

I'm a little skeptical about the radio having faulty electrolytics, but
they could have aged if it is an older radio. I would want to try a line
filter of some kind, just inside the radio. Perhaps as simple as putting
a 0.1 Microfarad 600 volt capacitor across the line, with leads as short
as practical. However, I recall cases where such a filter made things
worse!

Fred